Myths about Carrier Grade NAT (CGN), and Cisco options - Cisco ASR 1000 and ASR 9000 Router / BRAS

1. CGN has very good result, that with typical 444 deployment. If you are an ISP, your subscriber does not get any explicit public routable IPv4 address, saving your IPv4 space and the risk of your subscriber's PC being hacked.

2. Cisco ASR 1000 / 9000, Huawei NE, Juniper MX all support CGN within SP edge routers / BRAS. This is a big progress in last couple years because you easily get rid of separate firewalls just for NAT functions, saving extra single point of failure.

3. For sophisticated regions (Japan, US, Korea, etc), usually 1 single broadband / PPPoE subscriber consumes 1,500~2,000 CGN sessions; for emergent regions, the assumption is about 1,000. Therefore, better calculate this ratio carefully because if the overload is too heavy, the service quality would drastically be downgraded.

4. Cisco ASR 1000 routers uses RP to provide the CGN function so the maximum session is 6 million chassis-wide, meaning about max 6K CGN subscribers (not so big but good enough for starting private ISP). The ASR 9000 router has the ISM (new edition called VSM) line card. ISM card supports max 20 million sessions (already End-of-Life), and VSM card supports max 60 million session. This means if you need very large scale CGN and you want a centralized BRAS, ASR 9000 is a good option because it's all integrated. Basically, VSM is a dedicated "server" integrated in ASR9K chassis.

Morris Hagen, ICI Team - Network Expertise Helps You Succeed

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